Adds the common-layer IDecalQuery capability (spawn/remove/clear/count/setLimit with an opaque texture handle) provided by the decal module at construction, so editor/devtools can drive decals without linking the module; adds a Squirrel script test (decal.nut + DecalScriptTest) covering eve.Decal() getName/clearAll/setLimit/update, and a C++ capability consumer test.
